Content may be transmitted by a geosynchronous satellite communication network to users for decoding and playback. A system diagram of a typical satellite download link is illustrated in FIG. 1. The satellite downlink 100 includes a satellite antenna 102 connected to a low noise block converter (LNB) 104. The LNB is connected to a satellite receiver/decoder 106. The satellite can transmit signals including content channels modulated on a carrier. The content channels can be analog content channels or digital content channels. In many systems, data is modulated onto the same carrier using different polarizations. Where digital content channels are modulated onto a carrier, the digital data modulated on the carrier can include a plurality of digital content channels, each of which typically includes at least one video and/or audio stream.
In many instances, a signal containing multiple content channels is transmitted to a satellite network from an uplink facility. A transponder on the satellite then transmits a signal that can be received by a number of satellite antennas 102. The received signal is then passed to a LNB 104, which down converts the signal to an intermediate frequency (IF). Lastly, the IF signal is passed to a satellite receiver/decoder 106, such as a set top box, where the signal containing content is demodulated and decoded (i.e. audio and/or video) for playback.
In this way, information transmitted as relatively high frequency satellite signals, usually as microwave signals, may be converted to similar signals at a much lower frequency, usually known as an intermediate frequency (IF) compatible with the electronics of the decoding device and/or cabling used to connect an LNB to a satellite receiver/decoder. A content channel is the digital data modulated onto a carrier frequency within the IF signal. Users may then receive selected content channels as IF signals for decoding and use. Representations of the frequency spectra of signals during various stages in the down-conversion of satellite communication signals is illustrated FIGS. 2A, 2B and 2C.
Radio frequency (RF) signals are typically transmitted by a satellite to a receiver at high frequencies. A typical satellite radio frequency (RF) signal for downlinking is illustrated in FIG. 2A. As illustrated, the signal is transmitted at high frequencies, spanning from 11 GHz to 12 GHz. A satellite signal when received by a satellite signal receiver is usually weak after traveling great distances during transmission and is of a relatively high frequency. When signals are sent through coaxial cables, the higher the frequency, the greater the losses that occur in the cable per unit of length.
A LNB may be used to amplify and convert these high frequency signals to a lower, more manageable frequency. The frequency spectrum of satellite signals processed by a LNB is illustrated in FIGS. 2B and 2C. In Europe, the frequency spectrum of LNB processed signals may be from 950 MHz to 2150 MHz (see FIG. 2B). In the United States (U.S.), the frequency spectrum of LNB processed signals may be from 950 MHz to 1450 MHz (see FIG. 2C).
Signals containing content received from a satellite typically include multiple content channels in the frequency band of the carrier signal. Typical frequency spectrum for carrier frequencies of channels of encoded digital data carried by the IF signal processed by a typical LNB is illustrated in FIG. 2D. Here, the frequency band spans from 950 MHz to 2150 MHz or 1450 MHz and there are multiple 36/55 MHz content channels in this frequency band. In order for a user to decode selected media, an L-band tuner may be used to select the desired channel. For example, a certain carrier frequency may be selected where a 36/55 MHz band may be transferred to a receiver/decoder for use by the user.
LNBs can be implemented in many ways using many different LNB architectures. FIG. 3 illustrates a diagram of a typical universal LNB architecture with dual outputs. In this architecture, the LNB receives two RF input signals from the satellite. One signal is for the vertical polarization antenna 302 and the other is for the horizontal polarization antenna 304. For example, the frequency band of both signals may be from 10.7-12.75 GHz. The LNB first separates the signal into two bands with two band pass filters, a low band 306 (10.7-11.7 GHz) and a high band 308 (11.7-12.75 GHz). Low band signals are mixed down to 950-1950 MHz with local oscillator (LO) 310 at 9.75 GHz. The LO is the frequency used in the LNB to block convert the frequency of the satellite signal, or transponder frequency, to a lower frequency band. High band signals are mixed down to 1100-2150 MHz with LO 312 at 10.6 GHz. Output signals are selected from the four down converted L-band signals with a 4:2 multiplexer 314 in response to request for specific channels from the decode device. Using the Universal LNB illustrated in FIG. 3, viewers can only tune to content on two of the 1 GHz L-band channels at any time. Additional cables are required for users to watch content from one of the other two 1 GHz L-band channels.
Single cable LNB architectures have been developed to reduce the amount of cabling involved in providing a system that can provide content from all four of the 1 GHz L-band signals produced by the LNB. A diagram of a typical single cable LNB design supporting up to four satellite content channels in one cable is illustrated in FIG. 4. In the illustrated single cable LNB architecture, the LNB receives two RF input signals from the satellite in a manner similar to FIG. 3. One is for the vertical polarization antenna 402 and the other is for the horizontal polarization antenna 404. In many systems, the frequency band of both signals may be from 10.7-12.75 GHz. The LNB first separates the signal into two bands with two band pass filters, a low band 406 (10.7-11.7 GHz) and a high band 408 (11.7-12.75 GHz). Low band signals are mixed down to 950-1950 MHz with a LO 410 at 9.75 GHz. High band signals are mixed down to 1100-2150 MHz with a LO 412 at 10.6 GHz. Four content channels (i.e. a channel within the L-band signal containing digital data modulated onto a specific carrier frequency) from these four L-band signals are selected with a multiplexer 414 and mixed to four new carrier frequencies using four mixers. Four surface acoustic wave (SAW) filters 416 are then used to remove the unselected channels in the band.